Internal combustion engines of the so called jet-ignition or torch-ignition type generally provide a small ignition chamber adjacent the main combustion chamber for each cylinder and connected therewith by a small orifice. The main combustion chambers are supplied with air-fuel mixture chosen for economy, emissions reduction, etc. which may not be easily ignitable. The auxiliary chambers are supplied through separate induction means with a small volume of easily ignitable air-fuel mixture which is then ignited by a spark plug. Burning the mixture in the auxiliary chamber causes expansion through the orifice, resulting in a jet or flame extending into the main chamber which causes ignition and burning of the main charge.
While torch ignition engines have been known in the art for many years, they have not achieved wide commercial usage. In previous designs, the complexities caused by dual induction systems, intake valves, valve actuating mechanisms, and exhaust or other mixture heating devices have resulted in relatively complex engine constructions, adding to the cost of manufacture as well as requiring careful attention to manufacturing details to obtain the desired operating characteristics.